# Statistics: T-Test vs. Z-Test and 1 tailed vs 2 tailed test

So, I understand that when making confidence intervals the z test is for proportions and the t test is for mean. Is this true for hypothesis testing also? Also, if we are trying to find an interval for a mean but have a large sample and/or know standard deviation of the population do we use the z test instead or is it always the t test for mean? If you do not know population standard deviation for a proportion, do you use the t test or is it always the z test for proportion?

The other issue I'm having is the difference in steps in a one tailed vs two tailed test. Do you have to double the p value when doing a two tailed test? What is the difference in the steps involved between the two?

Sorry for a million questions and thanks ahead of time.

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